Problem

When two elements combine, they do so by transferring or sharing electrons to reach stable electron configurations. Aluminum has 3 valence electrons it readily loses, while sulfur has 6 valence electrons and needs 2 more to fill its outer shell. The key is balancing how many atoms of each element are needed so the total electrons lost equals electrons gained—that's how you determine the subscripts in the formula.

When two elements combine, they do so by transferring or sharing electrons to reach stable electron configurations. Aluminum has 3 valence electrons it readily loses, while sulfur has 6 valence electrons and needs 2 more to fill its outer shell. The key is balancing how many atoms of each element are needed so the total electrons lost equals electrons gained—that's how you determine the subscripts in the formula.